Skip to content
6CCVD Research

The Effect of Interlayer Microstructure on the Thermal Boundary Resistance of GaN-on-Diamond Substrate

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2022-05-14
JournalCoatings
AuthorsJia Xin, Lu Huang, Miao Sun, Xia Zhao, Junjun Wei
InstitutionsJiangsu Institute of Metrology, University of Science and Technology Beijing
Citations8
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study investigates the optimization of the SiNx interlayer microstructure to minimize the Thermal Boundary Resistance (TBR) in GaN-on-Diamond substrates, critical for high-power device heat dissipation.

  • Core Achievement: Successfully demonstrated that a periodically patterned SiNx interlayer significantly reduces the effective TBR (TBReff,Dia/GaN) compared to standard unpatterned layers.
  • Quantified Reduction: The patterned SiNx interlayer achieved a TBR of 32.2 ± 1.8 m2KGW-1, representing a 20% reduction compared to the original 100 nm SiNx layer (40.5 ± 2.5 m2KGW-1).
  • Mechanism of Improvement: The periodic structure (20 nm x 20 nm pits) increases the interface contact area, enhancing phonon transmission efficiency, similar to macroscopic heat sink fins.
  • Microstructural Benefits: Patterning improves the adhesion and bonding strength between SiNx and diamond, evidenced by a near-doubling of the critical load (Lc3 increased from 8 N to 15 N).
  • Growth Enhancement: The periodic structure promotes higher diamond nucleation density and reduces interfacial voids, leading to a thinner, denser, low-quality diamond nucleation layer (400 nm vs. 1 ”m).
  • Methodology: Thermal properties were accurately characterized using Time-Domain Thermoreflectance (TDTR) measurements, supported by cross-sectional TEM analysis.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Lowest Thermal Boundary Resistance (TBR)32.2 ± 1.8m2KGW-1GaN-on-Diamond with Periodic SiNx Interlayer
TBR (Original SiNx, 100 nm)40.5 ± 2.5m2KGW-1Baseline structure
TBR (SiNx, 80 nm)38.8 ± 1.5m2KGW-1Thinner unpatterned structure
SiNx Interlayer Thickness (Tested)80, 100nmBefore diamond growth
SiNx Periodic Structure Dimensions20 x 20nmCubic pits with 20 nm step length
Diamond Film Thickness (Target)2”mPolycrystalline layer grown by MPCVD
Diamond Nucleation Layer Thickness (Periodic Sample)~400nmObserved via cross-sectional TEM
Critical Load (Lc3) - Periodic SiNx15NAdhesion test (Micro-scratch)
Critical Load (Lc3) - Original SiNx8NAdhesion test (Micro-scratch)
Thermal Conductivity (Diamond, Fitted)~2000W/mKFitted parameter for TDTR analysis
Thermal Conductivity (GaN, Fixed)130W/mKFixed parameter for TDTR analysis
Thermal Conductivity (SiNx, Approx.)~1W/mKAmorphous nature of SiNx

Key Methodologies

Section titled “Key Methodologies”
  1. Substrate and Interlayer Deposition: SiNx interlayers (100 nm or 80 nm thick) were deposited onto standard GaN-on-Si wafers using Radio Frequency (RF) magnetron sputtering.
  2. Periodic Patterning: The 100 nm SiNx surface was patterned using Inductively Coupled Plasma (ICP) etching combined with a precise mask control method to create 20 nm x 20 nm cubic pits.
    • ICP Parameters: ICP/RF Power: 100 W/10 W; Chamber Pressure: 1 Pa; Gas Flows (O2/Ar/SF6): 5/10/10 Sccm.
  3. Diamond Seeding: All SiNx surfaces were ultrasonically soaked in nanodiamond solution (grain size ~5 nm) to achieve high nucleation density, followed by washing and drying.
  4. Diamond Growth: A 2 ”m polycrystalline diamond layer was grown using Microwave Plasma Chemical Vapor Deposition (MPCVD).
    • Nucleation: 5 min at 750 °C (12% CH4 concentration).
    • Growth: 120 min at 800 °C (5% CH4 concentration).
  5. Thermal Characterization (TDTR): A 100 nm thick Aluminum (Al) film was deposited on the diamond surface via electron beam evaporation to serve as the transducer/sensor layer. Time-Domain Thermoreflectance (TDTR) was used to measure the thermal signal and extract TBReff,Dia/GaN.
  6. Microstructural and Adhesion Analysis: Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to observe surface and cross-sectional morphologies. Adhesion strength was evaluated using a micro-scratch tester (continuous linear loading 0-20 N).

Commercial Applications

Section titled “Commercial Applications”

The optimization of the GaN-on-Diamond interface is crucial for industries requiring high-performance thermal management in semiconductor devices:

  • High Power RF and Microwave Devices: Essential for next-generation 5G/6G infrastructure, radar systems, and satellite communications, where GaN HEMTs must operate at high power densities without thermal runaway.
  • Power Electronics: Used in electric vehicles, industrial motor drives, and power supplies, where GaN devices offer superior efficiency, but require robust heat dissipation to maintain reliability.
  • Advanced Semiconductor Manufacturing: Provides a proven method for designing and fabricating high-quality GaN-on-Diamond substrates, replacing traditional substrates like SiC or Sapphire.
  • Thermal Management Solutions: The principle of using periodic microstructures to enhance interface bonding and phonon transport can be generalized to other heterogeneous material interfaces (e.g., thermal interface materials).
View Original Abstract

Diamond has the highest thermal conductivity of any natural material. It can be used to integrate with GaN to dissipate heat from AlGaN/GaN high electron mobility transistor (HEMT) channels. Much past work has investigated the thermal properties of GaN-on-diamond devices, especially the thermal boundary resistance between the diamond and GaN (TBReff,Dia/GaN). However, the effect of SiNx interlayer structure on the thermal resistance of GaN-on-diamond devices is less investigated. In this work, we explore the role of different interfaces in contributing to the thermal boundary resistance of the GaN-on-diamond layers, specifically using 100 nm layer of SiNx, 80 nm layer of SiNx, 100 nm layer of SiNx with a 20 nm × 20 nm periodic structure. Through combination with time-domain thermoreflectance measurement and microstructural analysis, we were able to determine that a patterning SiNx interlayer provided the lower thermal boundary resistance (32.2 ± 1.8 m2KGW−1) because of the diamond growth seeding and the diamond nucleation surface. In addition, the patterning of the SiNx interlayer can effectively improve the interface bonding force and diamond nucleation density and reduce the thermal boundary resistance of the GaN-on-diamond. This enables significant improvement in heat dissipation capability of GaN-on-diamond with respect to GaN wafers.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1993 - High electron mobility transistor based on a GaN/AlxGa1−xN heterojunction [Crossref]
  2. 2009 - An internally-matched GaN HEMTs device with 45.2 W at 8 GHz for X-band application [Crossref]
  3. 2021 - Fabrication of low stress GaN-on-diamond structure via dual-sided diamond film deposition [Crossref]
  4. 2015 - Self-heating profile in an AlGaN/GaN heterojunction field-effect transistor studied by ultraviolet and visible micro-Raman spectroscopy [Crossref]
  5. 2006 - Self-heating in a GaN based heterostructure field effect transistor: Ultraviolet and visible Raman measurements and simulations [Crossref]
  6. 2017 - Barrier-layer optimization for enhanced GaN-on-diamond device cooling [Crossref]
  7. 2018 - Simultaneous measurement of thermal conductivity and specific heat in a single TDTR experiment [Crossref]
  8. 2018 - Low Thermal boundary resistance interfaces for GaN-on-diamond devices [Crossref]
  9. 2019 - The influence of dielectric layer on the thermal boundary resistance of GaN-on-diamond substrate [Crossref]
  10. 2006 - Heat generation and transport in nanometer-scale transistors [Crossref]

Reads Similar to This

Efficient generation of nitrogen vacancy centers by laser writing close to the diamond surface with a layer of silicon nanoballs Power devices on bulk gallium nitride and diamond substrates - An overview of ARPA-E's SWITCHES program Photovoltaics literature survey (No. 147)